Characterization of the interfaces between ferromagnetic metals and organic films

Organic spintronics is a promising field in which organic materials are used to mediate and control the spin-polarized signal. The properties of the interface between the ferromagnetic metals and organic semiconductors are very important to the performance of the devices. While there is a lot of literature on the properties of interface between non-magnetic metal and organic materials, there is almost no work published on investigating the interface formed between ferromagnetic metal and organic semiconductors. This dissertation is designed to characterize the structural and magnetic properties of the interfaces between the ferromagnetic metals and organic thin films. The ferromagnetic metals were deposited on four different organic semiconductor as well as two types of self-assembled monolayers. The samples were studied by atomic force microscopy, x-ray reflectivity, magneto-optical Kerr effect and vibrating sample magnetometer. The results showed that the morphology and roughness of the underlayer had a great effect on the magnetic properties of the ferromagnetic metal thin film. The ferromagnetic metal thin film had a higher coercivity on rougher films and lower coercivity on smoother films. Based on the angular dependent measurements, they did not show any easy access or hard access. Temperature dependent magnetic measurements showed that the saturation magnetization and coercivity of the samples was stable from room temperature to 600 K. For the same thickness of Co, Ni and Fe on the same organic materials, Ni had the lowest coercivity while Fe had the highest. Fe tended to lose more magnetic signal due to it is the most reactive among the three. Ni tended to diffuse deeper into the organic materials because the atom could travel longer before it reacted with the organic materials. Benzoic acid derivative SAMs and fatty acid SAMs were made and Co thin films were deposited on them. Magnetic data showed that well-packed fatty acid SAMs could effectively prevent the Co diffusion.